FIG. 1 is a schematic of a large-screen video display. Three cathode-ray tubes, CRT, generate identical images. One image is typically red, one is green, and one is blue. Each CRT has an associated lens system and collimator, LC, which captures the CRT's image and projects it to a dichroic mirror, DCM. The DCM combines the three images, and a fourth lens system L projects the combined image to a display screen D, via a mirror M.
The large number of components in such a projection system imposes high cost. Further, the optical elements require precise mechanical alignment, which is expensive to both achieve and maintain. Also, all of the optical elements must be protected from ambient dust, which requires either periodic cleaning or enclosure in a dust-free container. The container imposes added cost, together with the problem (perhaps minor) of dissipating the heat generated by now-enclosed CRTs.
An alternate projection system is shown in FIG. 2. A light source 3 produces light 6 which is collimated by a lens system 9. The collimated light is projected through a liquid crystal display 12, which acts as a shutter. The liquid crystal display can be of the monochrome- or color type. A heat shield 11 protects the LCD from the heat of the light source 3.
FIG. 3 shows the shuttering operation. Some pixels 16 are dark, and eclipse the collimated light 6. Other pixels 18 are bright, and transmit the collimated light 6. In the example of FIG. 3, the letter "d" is generated on the display screen D. The collimated light is modulated pixel-by-pixel.
The alternate projection system contains fewer parts, compared with that of FIG. 1. The present invention is yet a further improvement of this alternate system.